Astrosat

Astrosat is India’s first dedicated multi-wavelength space observatory, launched by the Indian Space Research Organisation (ISRO) to study celestial objects and phenomena across different spectral bands, including ultraviolet, optical, and X-ray regions. It represents a significant milestone in Indian space astronomy, providing the nation with an advanced platform for high-energy astrophysical research comparable to international observatories such as NASA’s Hubble Space Telescope and ESA’s XMM-Newton.

Background and Development

The concept of Astrosat emerged from the need to establish an independent Indian space-based observatory capable of conducting multi-wavelength observations. Prior to Astrosat, India’s space research primarily relied on ground-based telescopes and international collaborations for astronomical data.
The project was approved in 2004, and after years of design, integration, and calibration, Astrosat was successfully launched on 28 September 2015 aboard the Polar Satellite Launch Vehicle (PSLV-C30) from the Satish Dhawan Space Centre, Sriharikota. It was placed in a 650 km near-equatorial orbit with an inclination of 6°, enabling stable observations with minimal background interference.
Astrosat was developed through collaboration between multiple Indian research institutions, including:

• ISRO Satellite Centre (ISAC), Bengaluru – responsible for satellite design and integration.
• Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune.
• Tata Institute of Fundamental Research (TIFR), Mumbai.
• Raman Research Institute (RRI), Bengaluru.
• Indian Institute of Astrophysics (IIA), Bengaluru.
• Space Applications Centre (SAC), Ahmedabad.

International collaboration was also involved, with contributions from the Canadian Space Agency (CSA) and the University of Leicester, United Kingdom.

Objectives

The main scientific goals of Astrosat include:

• Multi-wavelength observation of cosmic sources, including X-ray binaries, active galactic nuclei (AGN), supernova remnants, and galaxy clusters.
• Study of stellar evolution and star formation in the ultraviolet region.
• Monitoring of variable and transient celestial sources, such as gamma-ray bursts and black hole outbursts.
• Measurement of magnetic fields, temperature, and spectral properties of high-energy cosmic sources.
• Creation of a long-term database of ultraviolet and X-ray observations for global scientific use.

Payloads and Instruments

Astrosat is equipped with six scientific payloads, each designed to observe different parts of the electromagnetic spectrum simultaneously.

1. Ultraviolet Imaging Telescope (UVIT):
   • Captures images in far-ultraviolet (FUV), near-ultraviolet (NUV), and visible (VIS) wavelengths.
   • Provides high spatial resolution (up to 1.8 arcseconds).
   • Used to study young stellar populations, star-forming regions, and hot stars.
2. Soft X-ray Telescope (SXT):
   • Operates in the 0.3–8 keV energy range.
   • Uses focusing mirrors and an X-ray CCD detector to image cosmic X-ray sources.
   • Enables detailed spectral analysis of neutron stars, black holes, and supernova remnants.
3. Large Area X-ray Proportional Counter (LAXPC):
   • Sensitive to the 3–80 keV X-ray energy range.
   • Designed to study rapid variability and timing properties of X-ray binaries and pulsars.
   • Provides excellent timing resolution and large effective area for high-energy studies.
4. Cadmium Zinc Telluride Imager (CZTI):
   • Operates in the 10–150 keV hard X-ray band.
   • Capable of imaging, spectral studies, and polarimetry of bright X-ray sources.
   • Detects transient events such as gamma-ray bursts and solar flares.
5. Scanning Sky Monitor (SSM):
   • Continuously scans the sky in the 2.5–10 keV energy range.
   • Monitors and detects transient X-ray sources, providing alerts for follow-up observations.
6. Charged Particle Monitor (CPM):
   • Detects and monitors charged particles in the spacecraft’s environment.
   • Protects sensitive instruments from high-radiation exposure by triggering safety mechanisms.

Technical Specifications

• Launch Vehicle: PSLV-C30
• Launch Date: 28 September 2015
• Orbit Altitude: Approximately 650 km
• Inclination: 6°
• Mass: Around 1,515 kg
• Mission Life: Initially 5 years (extended due to excellent performance)
• Power Generation: Solar arrays producing about 700 W

Major Discoveries and Achievements

Astrosat has made numerous important contributions to astrophysical research:

• Discovery of new variable X-ray sources, including pulsars and binary systems.
• Observation of polarisation in hard X-rays, providing insights into the geometry and magnetic fields of cosmic sources.
• Simultaneous multi-band observations of active galactic nuclei and stellar flares.
• Detection of ultraviolet emissions from distant galaxies and star-forming regions, enhancing understanding of cosmic evolution.
• Contribution to gamma-ray burst studies, particularly in identifying afterglows and their temporal evolution.
• Monitoring of black hole systems such as Cygnus X-1 and GRS 1915+105, improving understanding of accretion dynamics.

Astrosat has also facilitated international collaborations by making data publicly accessible to researchers worldwide through the Indian Space Science Data Centre (ISSDC).

Significance

Astrosat represents a major leap for India in space-based astronomy and astrophysics, marking the country’s entry into the global league of astronomical observatories. Its ability to perform simultaneous multi-wavelength observations provides a comprehensive understanding of astrophysical processes that cannot be achieved through single-band studies.
The mission has significantly enhanced India’s scientific capabilities, fostering research collaborations and inspiring a new generation of space scientists. It has also demonstrated ISRO’s growing proficiency in developing complex, high-precision space science missions, paving the way for future projects such as XPoSat (X-ray Polarimeter Satellite) and Aditya-L1, India’s first solar observatory.